FWIW, I got this email from Penson today. (I'm sure there are others on this site who got the same notice.)
As you may know, Penson Worldwide, Inc. announced today that it has agreed to sell certain assets and liabilities of the futures division of its subsidiary Penson Financial Services, Inc. (âPenson Futuresâ) to Knight Execution & Clearing Services LLC ...In connection with this transaction, as of the close of business May 31, 2012, Penson Futures will assign your customer agreement to Knight and will also transfer your positions, segregated funds, 30.7 secured funds (if any) and trading account to Knight. Beginning June 1, 2012, your futures account will be held by Knight